THE ASTRONOMICAL ORIENTATION OF THE MAUSOLEUM OF GALLA PLACIDIA
IN RAVENNA
The Roman Mausoleums of Cecilia Metella, Augustus and Hadrian
(today’s Castel Sant'Angelo), and many other ones, have a square base podium
oriented towards the four cardinal points, which supports the circular main
building in the shape of a tower, where the actual tomb was.
We know that
the Mausoleum of Hadrian (today’s Castel Sant’Angelo) is also astronomically oriented
so that during the days of the Summer Solstice, special illuminations occurr
inside its Hall of the Burial Urns, as explained in the book by Marina De Franceschini
«Castel Sant’Angelo. Mausoleum of Hadrian. Architecture and Light» (English
edition) which reveals its symbolic meaning.
The same can be said for the Mausoleum of Galla Placidia, whose astronomical
orientation was discovered and calculated by Manuela Incerti and published online
in the article «The Mausoleum of Galla Placidia in Ravenna: Archaeoastronomy, Numbers,
Geometry and Communication» (in English language).
The study explains that the main axis of the Mausoleum
is oriented north-south, with the entrance to the north, and an azimuth
of 180.2°. Therefore the east and west transverse niches are supposed
to have an azimuth of 90° and 270°; but the plan shows that they are not
orthogonal but slightly oblique.
The Laser scanner in fact detected an azimuth of 94.3°
for the east niche.
The azimuth, (as Incerti explains) corresponds to the sunset
of two special dates, March 26-27 and September 13-14 of the time when the
Mausoleum was built, that is, between 425 and 450 AD. The first date is
close to March 25, the Annunciation of Mary; the second to September 14, the
feast of the Holy Cross, of which Galla Placidia possessed a relic, to which
she was particularly devoted. And in fact she built the Basilica di Santa
Croce next to the Mausoleum
From the text of the article it is not
clear whether on those dates any illuminations (hierophanies) were seen; the
light had to enter from the windows of the lunettes of the east and west niches,
because they occurred at dawn and sunset, when the Sun is lowest; the windows
of the lunettes of the turret were located too high for that purpose. Currently
all the windows are closed by semi-transparent alabaster slabs that, however,
prevent the rays of the Sun from creating beams of light.
At midday on the Winter Solstice, moreover, the Sun's rays enter from the south
side, from the window high up in the lunette of the turret, and illuminate the
portal: this illumination still occurs today (Incerti p. 497). The hierophany
with the ray of light illuminating the north portal at midday is similar to
the one we know in the Pantheon, where however it occurs on April 21 (Dies Natalis
of Rome).
This means that the Mausoleum of Galla Placidia followed
a centuries-old tradition of astronomical orientation and sacred symbolism.
The symbols of pagan cults were kept in use because in an illiterate world
they were understandable to everyone, although they were given a different meaning
to adapt them to the Christian cults.
As for the architecture, the
scheme of the Etruscan Templum with the square containing a circle was preserved.
Its symbolic meaning remained linked to the celestial vault: in the pagan world
the circle represented the Cosmos, in the early Christian one it represents
the Sky, which contains the Cross, that is the salvation that comes from God.
The analogies with the Hall of the Burial Urns of the Mausoleum of Hadrian,
which Galla Placidia certainly knew, are notable: both are oriented towards
the four cardinal points, have a cross plan with an access dromos from the north
and three niches for as many sarcophagi. In both of them the hierophanies are
created by the east and west windows.
As for the astronomical orientation
and the symbolic meaning of the hierophanies, the choice of dates reflects
the transition from pagan cults to Christian cults.
In the Mausoleum
of Hadrian the windows of the Hall of the Burial Urns are oriented to the east
and west, and still today create hierophanies on the days of the Summer Solstice.
The symbolism of that date was linked to the deified Emperor Hadrian, depicted
as Sol Invictus driving the Quadriga of the Sun, and consequently to
the imperial cult which was a legitimation of the dynastic succession to power.
The deified emperor chose his successor and legitimized him with the hierophany,
as explained in the book of Marina De Franceschini cited above.
In the
Mausoleum of Galla Placidia, the hierophanies could be produced from the east
and west side windows, just like in Castel Sant’Angelo, but the orientation
was calculated so that they could be seen on two dates linked to the Christian
cults of the Madonna and the Holy Cross.
The illumination of the portal
of the Mausoleum in Ravenna at the Winter Solstice, which is still visible,
coincides with December 25, the birth date of Jesus Christ, that overlapped
with the date on which Sol Invictus was originally celebrated.
Over the centuries the hierophanies kept their symbolic meaning
of «sacred apparition», where the Light is a symbol of the divine presence.
Jesus himself said «I am the Light of the world; whoever follows me will
not walk in darkness, but will have the Light of Life». (John 8:12).
Even if we are in a different Christian context, the hierophanies kept giving
a sacred legitimacy to the imperial succession, because the emperor was
“blessed” by the divine Light.
At the beginning of 1200 the chancellor
of the school of Chartres, Pierre de Roissy wrote: «The windows are divine
scriptures because they pour the light of the true Sun, that is, of God,
inside the Church, in the hearts of the faithful, illuminating them at the
same time».
This is why several churches of early Christian era were
designed to obtain illuminations on certain days of the year. For example
in the church of San Paragorio in Noli (Savona) on the days of the
Summer Solstice a ray of light moves along the walls and the apse
until it illuminates the tabernacle for a few minutes. In other churches
the hierophanies are seen in the days of feasts celebrated in honor
of the saints to whom they are dedicated.
Astronomical orientation thus continued to have an important
symbolic significance in Late Antiquity and the Middle Ages.